Self sustaining energy system for a building

ABSTRACT

A self sustaining energy system for a building is provided part of which is typically driven by geothermal energy. The energy system typically uses a ground source heat pump for heating and cooling the building airspace and an organic Rankine cycle drive for producing electricity. A solar powered heating system may also serve as a heat source for providing domestic hot water and supplemental airspace heating.

CROSS REFERENCE TO RELATED APPLICATION

This applications claims priority from U.S. Provisional PatentApplication Ser. No. 61/416,603, filed Nov. 23, 2010; the disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to a total self sufficientenergy system typically including a heating and cooling system. Moreparticularly, the present invention relates to a self sustaining systemfor heating and cooling a building, providing hot water for the buildingand generating electricity for the building electrical system.Specifically, the invention relates to such a system which utilizessolar energy, an organic Rankine cycle which is driven by geothermalenergy, and a ground source heat pump.

2. Background Information

The heating and cooling of buildings in a manner which provides adesirable work environment increases productivity and job satisfactionwhile reducing absenteeism. However, the heating and cooling ofbuildings represents a substantial consumption of energy, with someestimates indicating about 40% of global energy consumption. Thus, thereis always a need for improving the energy efficiency of such heating andcooling systems. Furthermore, there are various energy regulations andstandards in various countries mandating specific goals. For example,the European Union Building Performance Directive requires net-zeroenergy by 2019 for all new buildings, and carbon neutrality by 2019 forall new commercial buildings. By way of further example, new andrenovated buildings in the United States must achieve 55% fossil fuelreduction targets in 2010 and be carbon neutral by 2030. Future federallegislation may apply additional requirements in the United States.Meanwhile, various state and local governments have already passedpertinent regulations, such as in New York and California. Thus, thereis a need in the art to improve the efficiency of heating and coolingsystems for buildings both in order to minimize electric energy costsand to meet various regulations. The present invention addresses thisneed.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an energy system comprising a heat pumpcomprising a first earth-coupled heat exchanger; an electric motoroperatively connected to the heat pump; an organic Rankine cycle drive;a second earth-coupled heat exchanger which provides a geothermal heatsource for the organic Rankine cycle drive; and an electric generatordriven by the organic Rankine cycle drive and in electricalcommunication with the motor.

The present invention also provides a method comprising the steps ofoperating an electric motor to circulate a working fluid in a heat pumpwhich comprises a first earth-coupled heat exchanger; providing ageothermal heat source for an organic Rankine cycle drive with a secondearth-coupled heat exchanger; driving an electric generator with theorganic Rankine cycle drive to produce electricity; and using theelectricity to power operation of the electric motor.

The present invention further provides an energy system comprising afirst earth-coupled heat exchanger configured to absorb heat energy fromsoil; and a second earth-coupled heat exchanger configured to releaseheat energy to the soil to prevent the soil from freezing as a result ofthe heat energy absorbed by the first heat exchanger.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A preferred embodiment of the invention, illustrated of the best mode inwhich Applicant contemplates applying the principles, is set forth inthe following description and is shown in the drawings and isparticularly and distinctly pointed out and set forth in the appendedclaims.

FIG. 1 is a diagrammatic view of the energy system of the presentinvention.

FIG. 2 is a diagrammatic view similar to FIG. 1 in which the energysystem of the present invention uses an alternate heat pumpconfiguration.

Similar numbers refer to similar parts throughout the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The self sustaining energy system of the present invention is showngenerally at 10 in FIG. 1 with an alternate embodiment shown generallyat 10A in FIG. 2. System 10 is configured to provide energy to abuilding 12 which defines an enclosed building airspace 14. Airspace 14may be divided into multiple compartments such as rooms or units whichare part of a recirculation loop of air provided by ducts in betweenthese respective rooms. System 10 includes an airspace heating andcooling system in the form of a ground source heat pump (GHP) 16Aconfigured for heating and cooling airspace 14. System 10 furtherincludes a solar-powered heating system 18 which is in part configuredto provide domestic hot water (DHW) to building 12. System 10 furtherincludes an electricity generation system 20 configured to provideelectrical energy needed to building 12. Each of systems 16, 18 and 20utilizes an earth-coupled heat exchanger as described further below.Building 12 is built on top of the ground, earth or soil 22 and may bepositioned above an aquifer 24 typically far below an upper surface 26of the ground or soil 22. Various components of systems 10, 10A may beabove ground or underground and may include above-ground portions andunderground portions, respectively above and below surface 26. Althoughthese portions may not be specified herein elsewhere, such terminologyis applicable to these various components or portions, as will beevident from the Figures. To take advantage of ground source heat orgeothermal heat, one or more boreholes such as boreholes 28A and 28B aretypically bored into the earth extending downwardly from upper surface26 either directly beneath building 12 or adjacent building 12. It willalso be appreciated that the portion of upper surface 26 which isdirectly below building 12 may be substantially lower than that portionwhich extends outwardly from building 12, such as when building 12includes a basement and/or underground parking deck.

The airspace heating and cooling system or GHP 16A includes anearth-coupled heat exchanger 30A which extends downwardly withinborehole 28A below surface 26 and is in the exemplary embodimentdirectly below building 12. Heat exchanger 30 is part of a tubularclosed recirculation loop through which is circulated a working fluidfor moving heat energy to and from soil 22 and a water cooled condenser32 of GHP 16A. The working fluid may be a water-antifreeze solution(such as a water-glycol solution), brine or other water based solutionor any other suitable working fluid. GHP 16A further includes a separateclosed recirculation loop which includes condenser 32, an air cooledcondenser 34, and in which a turbo compressor 36 may be disposed suchthat turbo compressor 36 is operatively connected to and driven by anelectric motor 38. Condenser 34 includes an air intake and air exhausteach in fluid communication with airspace 14 to allow for air to flowthrough condenser 14 and for air recirculation within airspace 14 asindicated at arrows A.

Solar-powered heating system 18 includes thermal solar collectors 40which are exposed to sunlight during the day and are typically locatedon the roof of the building. System 18 further includes or isinterconnected with a domestic hot water (DHW) system 42 which includesa pump 44, a hot water tank 46 and appropriate piping or water pipes 48which provide recirculation loops in combination with pump 44 and tank46 and also lead to the various water taps (which may include or feedshowers, hot tubs, whirlpool baths or Jacuzzis, swimming pools, etc.)within or otherwise adjacent building 12. Water pipes 48 also include anunderground pipe or earth-coupled heat exchanger 50 which extends belowsurface 26 within soil 22 and borehole 28B. A thermal storage tank 51 isalso provided and typically has thermally insulated walls defining aninterior chamber 53 with a phase change material (PCM) 55 therein. Tank51 is shown as an underground tank although tank 51 may also be aboveground. Water pipes 48 extend into tank 51 and thus include a loop orheat exchanger 57 which is within interior chamber 53 and is in directcontact with and surrounded by PCM 55. PCM 55 changes phase by meltingor solidifying typically at a melting or freezing phase changetemperature in the range of about 80° F. to 300° F. While material 55may be a good heat absorbing material able to absorb or release asubstantial amount of heat energy even without changing phase, it ispreferably a phase change material so that the latent heat of fusionprovides substantial thermal storage during the phase change. In oneembodiment, PCM 55 may be a paraffin, paraffin wax or black wax paraffinalthough other suitable materials may be used.

Electricity generation system 20 includes an organic Rankine cycle (ORC)drive 52 configured to drive the generation of electricity. ORC drive 52includes a ground-coupled heat exchanger 54 which is part of a tubularclosed recirculation loop which circulates an appropriate working fluidand which serves as a heat sink. A portion of the recirculation loopwhich serves as heat exchanger 54 is, like the other earth-coupled heatexchangers, underground and is shown here in borehole 28A, although itmay be in a separate borehole. Heat exchanger loop 54 may extend intoaquifer 24 whereby aquifer 24 and/or soil 22 serves as the heat sourcefor ORC drive 52. Pump 56 is also provided to pump the working fluidthrough the recirculation loop including the heat exchanger 54. Thisrecirculation loop also passes through a heat exchanger 58, which ispart of ORC drive 52. ORC drive 52 may be a relatively simple organicRankine cycle drive or may be a more complex one. FIG. 1 illustrates ORCdrive 52 as a relatively simple organic Rankine cycle which includes theclosed recirculation loop for recycling the refrigerant or refrigerantmixture to pass through heat exchanger 58, to drive rotation of aturbine 60, which is within the closed loop and drivingly coupled togenerator 62, and through a condenser 64 and a pump 66. In the exemplaryembodiment, this recirculation loop includes a ground loop 30C whichextends downwardly within another borehole 28C and which is anotherearth-coupled heat exchanger which serves as heat exchanger 64. Variousrefrigerants or refrigerant mixtures known in the art may be used withinthis recirculation loop. In the exemplary embodiment, the preferredrefrigerant mixtures are those described in U.S. patent application Ser.No. 12/406,187 of the present inventor entitled Power Generator Using anOrganic Rankine Cycle Drive With Refrigerant Mixtures and Low Waste HeatExhaust As a Heat Source, which has also published as U.S. PatentApplication Publication No. 2010/0126172, which is incorporated hereinby reference for all purposes. Simple and more complex organic Rankinecycle drives are described in greater detail in the above noted PatentApplication Publication (2010/0126172), and may be used in the presentinvention. Generator 62 is in electrical communication with the buildingelectrical system 68, which is represented diagrammatically and whichtypically includes electrical outlets throughout the building which areavailable to electrically power various electrical appliances and otherelectrical machinery within or adjacent building 12.

FIG. 1 further illustrates that heat exchangers 30A and 30C extenddownwardly below upper surface 26 by a depth D1 which is typically inthe range of about 5 to 10 feet. At a depth of about 6 feet, the groundtemperature is usually on the order of about 45° F. to 48° F. althoughthis may vary somewhat. FIG. 1 also illustrates that heat exchanger 50extends downwardly into soil 22 a depth D2 which is typically roughlythe same as depth D1 although this may vary somewhat. Heat exchanger 54extends much deeper into the ground as indicated by depth D3, which istypically on the order of 1500 to 2000 feet and is usually at least 500or 1000 feet.

Referring now to FIG. 2, system 10A is fairly similar to system 10except that system 10A uses a modified ground source heat pump 16Binstead of heat pump 16A. Heat pump 16B utilizes a direct exchange (DX)ground loop or earth-coupled heat exchanger 30B which is part of theheat pump's refrigerant loop buried underground. Thus, the working fluidwithin the loop (which is the same as described above for heat pump 16A)flows through a single recirculation loop including heat exchanger 30Band air cooled condenser 34. As with heat pump 16A, electric motor 38 isdrivingly connected or coupled to compressor 36 to power or driverotation of compressor 36, which pumps the working fluid through therecirculation loop in which compressor 36 is disposed.

The operation of systems 10 and 10A is now described starting withreference to FIG. 1. Generally, working fluid is circulated by asuitable pump through the recirculation loop which includes heatexchanger 30A and condenser or heat exchanger 32. Meanwhile, workingfluid is also circulated through the recirculation loop which includescondenser or heat exchanger 32 and condenser or heat exchanger 34. Atthe same time, air is blown with appropriate fans or blowers throughheat exchanger 34 via its intake and exhaust to circulate through therecirculation loop or loops within airspace 14 as shown at arrows A. Inthe heating mode of heat pump 16A, working fluid passing through heatexchanger 30A absorbs heat from soil 22 and any water within soil 22 andcarries it to heat exchanger 32 whereby the heat energy is released viaheat exchanger 32 to the working fluid within the other recirculationloop, which circulates to condenser or heat exchanger 34 to likewiserelease heat energy to the air circulating at arrows A in order to heatthe air within airspace 14. As previously noted, rotation of turbocompressor 36, which pumps the working fluid for circulation within thelatter recirculation loop, is driven by the rotational drive of motor38, which is powered by electricity which may be supplied or fed fromelectrical system 68. Motor 38 is typically in electrical communicationwith generator 62 via electrical system 62. Thus, heat pump 16 may bepowered by electricity produced by the ORC drive via turbine 60 andgenerator 62, which is operatively connected to and driven by the ORCdrive. In the air cooling mode, heat pump 16A is operated so that theworking fluid within exchanger 30A rejects heat into the ground which isdelivered there via the working fluid from exchanger 32. Thus, theworking fluid within this recirculation loop absorbs heat within heatexchanger 32 from the working fluid circulating in the otherrecirculation loop which includes the exchanger 34. Recirculation of air(arrows A) through heat exchanger 34 thus involves a transfer orrejection of heat from the air to the working fluid within condenser 34so that the air is cooled. Heat from air within the building isultimately transferred and rejected to the soil 22 via the heatexchanger 30A. This process thus cools the air being exhausted from heatexchanger 34 in order to cool the air within building 12 while alsorejecting heat to soil 22 and water therein to prevent freezing of thissoil and water, such as may result from transfer of heat energy fromsoil 22 to the working fluid in heat exchangers 30C and 54 and thus toORC drive 52.

Turning to FIG. 2, heat pump 16B provides the similar overall result ofheating or cooling air within airspace 14 and either rejecting heat toor releasing heat from soil 22 via heat exchanger 30B. The directexchange arrangement of heat pump 16B utilizes a single closed loopinstead of the two separate closed loops of heat exchanger 16A. Thus, inthe air heating mode, the working fluid within heat exchanger 30Babsorbs heat from soil 22 and releases heat to the circulating air atexchanger 34 to heat the air within building 12. In the cooling mode,the working fluid within this recirculation loop rejects heat to theground or soil 22 via exchanger 30B and absorbs heat from thecirculating air in airspace 14 at exchanger 34 in order to cool the aircirculating through exchanger 34 and into airspace 14. Rejection of heatto the ground via exchanger 30B may also prevent freezing of soil 22 asnoted above.

It is further noted that outside air may be mixed with the inside airwithin airspace 14. More particularly, heat pumps 16A, 16B may include adesuperheater which may be used to heat outside air which is mixed withthe inside air typically for the purpose of dehumidification. Thedesuperheater may also be used to heat water and thus produce hot water,which would typically be the case if hot water otherwise runs out.

The operation of solar-powered heating system 18 is now described withreference to either FIG. 1 or FIG. 2. The solar collectors 40 absorbheat energy from sunlight (represented by the arrows adjacent collectors40) and reject the heat therefrom to potable water flowing through pipes48 in order to heat the water so that hot water subsequently flowsthrough pipes 48 into hot water tank 46. The heated water within system42 remains at a temperature below the boiling point of water and thusremains in a liquid state. In the embodiment shown, pump 44 pumps waterfrom tank 46 and/or various portions of pipes 48 into the heat exchangerof solar collectors 40. It is noted that a thermosyphon arrangement mayalso be provided in which the water storage tank 46 is higher thanthermal collector 40 whereby the need for pump 44 is eliminated. Inaddition to providing potable water to the various taps of building 12,hot water is also circulated through the heat exchanger 50 whereby heatis rejected from the water within exchanger 50 to soil 22 adjacentexchanger 50. It is noted that boreholes 28A and 28B may be backfilledwith soil or other material so that the pipes or tubes are in directcontact with the soil and water within the soil. The purpose forproviding heat exchanger 50 is to prevent the ground or soil fromfreezing as a result of heat which is rejected from the soil primarilyvia heat exchanger 30A or 30B during operation of the respective heatpump 16 in the air heating mode and also via heat exchanger 54.

Hot water also flows through pipes 48 into thermal storage tank 51 whereheat is rejected from the solar heated water to PCM 55 via the heatexchanger 57 loop of pipes 48. Generally, thermal storage tank 51 isused for heat storage during the day and heat discharge during the nightto ensure full 24/7 supply of domestic hot water to building 12. Moreparticularly, heat energy rejected from the hot water to PCM 55 isstored in PCM 55, which is insulated against heat loss by the thermalinsulation in the walls of tank 51. Subsequently, when there is a needto heat water within system 42 which has dropped below a predeterminedthreshold temperature and when solar heating of the water directly viathe heat exchanger of thermal solar collectors 40 is no longer possibleor is not sufficient (such as at night time or during certain weatherconditions), the heat energy stored in PCM 55 is rejected to water inheat exchanger 57 to heat the undesirably cooled water to a chosendesired temperature sufficiently above the threshold temperature to besuitable for use as domestic hot water.

Typically, the heat rejected from hot water to PCM 55 via heat exchanger57 will cause all or part of PCM 55 to change phase by melting, therebystoring a relatively large amount of heat energy as latent heat offusion, although as previously noted, material 55 may nonetheless storea substantial amount of heat energy even without melting. Later, whenthe water below the threshold temperature absorbs heat from PCM 55 whencirculated through heat exchanger 57, all or part of PCM 55 typicallychanges phase from liquid to solid, thus again providing a substantialamount of heat energy via latent heat of fusion although heat energy maylikewise be transferred from PCM 55 at temperatures both above and belowits melting or freezing temperature.

Although the Figures show that water in pipes 48 is circulated throughheat exchanger 57, other fluids or liquids may be used to circulate in asimilar or separate recirculation loop passing through the heatexchanger of thermal solar collectors 40 to absorb heat therefrom andthrough a heat exchanger analogous to heat exchanger 57 within thermalstorage tank 51 to likewise release heat to PCM 55 for storage thereof.Then, relatively cooler water may be circulated through heat exchanger57 to absorb heat from PCM 55 to heat the water to a temperaturesuitable for use as domestic hot water in building 12. The use ofcertain fluids or coolants other than water in such a separaterecirculation loop may be useful at various temperatures, and certainlywould be appropriate at relatively higher temperatures which would causewater to boil. Such other liquids or coolants may thus also be used totransfer heat from the solar powered heating system to the ground viaheat exchanger 50.

Although solar powered heating system 18 is described here primarily asbeing used to supply heat for the domestic hot water system, it may alsobe used as a supplemental heat source for heating airspace 14. Thus,system 18 may include a solar-heated heat exchanger with suitableducting and a fan to blow air across the heat exchanger whereby system18 rejects heat via the heat exchanger to the air so that the heated airmay be circulated within airspace 14.

The operation of electricity generation system 20 is now described. Pump56 is operated to circulate the working fluid within the closed loopwhich includes earth-coupled heat exchanger 54 in order to absorb heatfrom soil 22 and/or aquifer 24 typically at the depths noted withrespect to depth D3 as well as all along the borehole to provide ageothermal heat source for the ORC drive 52. The working fluid flowswithin heat exchanger 58 and rejects heat to the refrigerant within theother closed recirculation loop, which is circulated therethrough viapump 66. As described in greater detail in the above noted patentapplication publication, the working fluid within this closed loopdrives the rotation of turbine 60, which in turn drives the rotation ofgenerator 62 to produce electrical energy or electricity, whereby anelectric current runs from generator 62 to the building electricalsystem 68 such that the electrical current is available to powerelectrically powered devices within or adjacent building 12. Heat energyin the working fluid in the loop of ORC drive 52 which includes turbine60 is rejected to the ground via heat exchanger 30C, thereby cooling theworking fluid and also preventing or helping prevent freezing of aportion of the ground which may otherwise occur as a result of heatenergy being rejected from this portion of the ground via heatexchangers 54 and/or 30A or 30B.

It is further noted that energy systems 10 and 10A may include abranching recirculation loop configured to transfer heat energy fromaquifer 24 and/or the soil along borehole 28A via heat exchanger 54 toPCM 55 within thermal storage tank 51. More particularly, such abranching recirculation would be connected to and branch off from theloop which includes heat exchanger 54 and extend into interior chamber53 to serve as a heat exchanger similar to heat exchanger 57 except thatthe working fluid used in this branching recirculation loop would be thesame as that circulating through heat exchangers 54 and 58. This optionmay, for instance, be useful when there is no demand or a decreaseddemand on ORC drive 52 to produce electricity.

Thus, systems 10 and 10A provide a self sustaining configuration forproviding various energy to building 12. More particularly, each ofthese systems provide the air heating and cooling system or heat pump, asolar-powered domestic hot water system, and an ORC-driven electricalgeneration system, each of which is coupled to the earth or soil toeither reject heat energy to the earth or soil or absorb heat energytherefrom. Energy systems 10 and 10A are highly efficient and thussubstantially reduce operating costs.

In the foregoing description, certain terms have been used for brevity,clearness, and understanding. No unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art because suchterms are used for descriptive purposes and are intended to be broadlyconstrued.

Moreover, the description and illustration of the invention is anexample and the invention is not limited to the exact details shown ordescribed.

1. An energy system comprising: a heat pump comprising a firstearth-coupled heat exchanger; an electric motor operatively connected tothe heat pump; an organic Rankine cycle drive; a second earth-coupledheat exchanger which provides a geothermal heat source for the organicRankine cycle drive; and an electric generator driven by the organicRankine cycle drive and in electrical communication with the motor. 2.The energy system of claim 1 further comprising a building defining anairspace; an air intake of the heat pump in fluid communication with theairspace; and an air exhaust of the heat pump in fluid communicationwith the airspace.
 3. The energy system of claim 1 further comprising acompressor of the heat pump; wherein the electric motor is operativelyconnected to the compressor.
 4. The energy system of claim 1 wherein theorganic Rankine cycle drive comprises a third earth-coupled heatexchanger configured to reject heat to the ground.
 5. The energy systemof claim 1 further comprising a third earth-coupled heat exchangerconfigured to release heat energy to the ground to prevent the groundfrom freezing as a result of the heat energy absorbed from the ground byat least one of the first and second earth-coupled heat exchangers. 6.The energy system of claim 5 further comprising a solar powered heatingsystem coupled to the third earth-coupled heat exchanger whereby thesolar powered heating system is configured to reject heat to the thirdearth-coupled heat exchanger.
 7. The energy system of claim 6 furthercomprising a domestic hot water system coupled to the solar poweredheating system whereby the solar powered heating system is configured toreject heat to water in the domestic hot water system.
 8. The energysystem of claim 7 further comprising a thermal storage tank; a phasechange material within the tank; and a portion of the domestic hot watersystem which extends adjacent the tank whereby the water within thedomestic hot water system is configured to reject heat to and melt thephase change material.
 9. The energy system of claim 5 furthercomprising a thermal storage tank; a phase change material within thetank; a recirculation loop in fluid communication with the thirdearth-coupled heat exchanger; a fluid within the recirculation loop; anda portion of the recirculation loop which extends adjacent the tankwhereby the fluid within the recirculation loop is configured to rejectheat to and melt the phase change material.
 10. The energy system ofclaim 5 wherein the organic Rankine cycle drive comprises a fourthearth-coupled heat exchanger configured to release heat energy to theground.
 11. The energy system of claim 1 further comprising a domestichot water system comprising an underground pipe configured to releaseheat energy to the ground to prevent the ground from freezing as aresult of the heat energy absorbed from the ground by at least one ofthe first and second earth-coupled heat exchangers.
 12. The energysystem of claim 11 further comprising a solar powered heating systemcoupled to the domestic hot water system whereby the solar poweredheating system is configured to reject heat to the domestic hot watersystem.
 13. The energy system of claim 1 wherein the secondearth-coupled heat exchanger extends into an aquifer.
 14. The energysystem of claim 1 wherein the second earth-coupled heat exchangerextends into the ground to a depth of at least 500 feet.
 15. The energysystem of claim 1 further comprising a first borehole formed in earthbeneath a building; wherein one of the first and second earth-coupledheat exchangers is within the first borehole.
 16. The energy system ofclaim 1 wherein the organic Rankine cycle drive comprises a thirdearth-coupled heat exchanger configured to release heat energy to theground.
 17. A method comprising the steps of: operating an electricmotor to circulate a working fluid in a heat pump which comprises afirst earth-coupled heat exchanger; providing a geothermal heat sourcefor an organic Rankine cycle drive with a second earth-coupled heatexchanger; driving an electric generator with the organic Rankine cycledrive to produce electricity; and using the electricity to poweroperation of the electric motor.
 18. The method of claim 17 furthercomprising cooling a portion of the ground by releasing heat from theportion of the ground to at least one of the first and secondearth-coupled heat exchangers; heating a third earth-coupled heatexchanger with a solar powered heating system; and rejecting heat fromthe third earth-coupled heat exchanger to the cooled portion of theground.
 19. The method of claim 17 further comprising rejecting heatfrom the organic Rankine cycle drive to the ground with a thirdearth-coupled heat exchanger.
 20. An energy system comprising: a firstearth-coupled heat exchanger configured to absorb heat energy from soil;and a second earth-coupled heat exchanger configured to release heatenergy to the soil to prevent the soil from freezing as a result of theheat energy absorbed by the first heat exchanger.